Hygroscope.



H. H. S. GUNYNGHAME.

' HYGROSOOPB APPLICATION FILED JAN. 26, 1911.

1,019,767. r Patented Mar.12,19l2.

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-Z1 V I f fnven/ar Afforney COLUMBIA PLANUGFIAFH C0..WASIIINOTQN, u,c

UNITED STATES PATENT OFFICE.

HENRY HARDINGE SAMUEL CUNYNGHAME, OF NUTFIELD, ENGLAND.

HYGROSGOPE.

To all whom it may concern:

Be it known that I, HENRY HARDINGE SAMUEL CUNYNGHAME, K. O. B., asubject of the King of Great Britain and Ireland,

residing at Nutfield, in the county of Surrey, England, have inventedImprovements in Hygroscopes, of which the following is a specification.

This invention relates to a hygroscope whereby it can be seen byinspection, without reference to tables, whether at the moment of takingthe observation the water vapor contained in the atmosphere exceeds orfalls below some definite specified proportion of the quantity necessaryto saturate it at the time the observation is made; or, alternatively,whether at the time of observation the water vapor contained in theatmosphere exceeds or falls below some definite specified weight in acubic foot or meter thereof. The instrument can be constructed so as toshow the above information, within the ranges of observation usualtohygrometers for any proportions desired, as for example 60 per cent.of humidity, or 2 grains to the cubic foot. These methods of expressinghumidity are well understood and in common use at the present time. Theinstrument is intended by this means to enable an observer to predictfrost, or to tell whether a room, factory or other place in doors or outof doors is in such a condition as to dryness or dampness as he desires.For this purpose according to one way of carrying out the invention twothermometers of ordinary form, consisting of bulbs and stems of glasscontaining mercury or other liquid, similar to those used in the wellknown wet and dry bulb hygrometer, are placed with their stems in closejuxtaposition, the stem of one or both being, when necessary, bent toallow the stems to be arranged close together side by side. One of themis arranged as a wet bulb thermometer with a piece of damp cloth orother means of cooling it by the evaporation of water. The other is adry bulb thermometer. The graduation of the stems of the twothermometers is however 5 not identical as to the size of division corresponding to a degree. Nor is the size of the divisions of eachthermometer a matter of indifference. On the contrary, the relativesizes of the divisions are in the two instruments carefully regulated ina proportion to i be hereinafter described, and the stems areSpecification of Letters Patent.

Application filed January 26, 1911.

Patented Mar. 12, 1912.

Serial No. 604,871.

put vertically in juxtaposition in a certain manner also to behereinafter described. Thus arranged, all the observer has to do, inmaking his observation, is, without necessarily noting the temperaturereading of either thermometer, simply to observe whether the top of thecolumn of liquid in the stem of the one does or does not standhorizontally above the top of the column of liquid in the stem of other.The division of the stems of the thermometers and the relative positionsof the stems when placed along side each other, are arranged tocorrespond with the purpose for which the instrument is to be used. Forexample, let it be supposed that it is desired to make a frostpredictor. When the temperature of the air out of doors is low, and atthe same time the quantity of water-vapor in the air is below about 2.4grains to the cubic foot, the amount of water vapor in the air will betoo small to check a heavy radiation of heat from the earth andtherefore a frost may be expected. Now when in an ordinary wet and drybulb hygrometer, the wet bulb reads 37 F. and the dry bulb reads 38 F.,the amount of water vapor present in the air is very nearly 2.4 grainsto the cubic foot. Again, when the wet bulb reads 45 F. (or eightdegrees higher than before) and the dry bulb reads 54 F. (or 16 degreeshigher than before) the amount of water vapor in the air is also verynearly 2.4 grains to the cubic foot, and for any proportionatelyintermediate figures such as 40 F. of the wet bulb (or 3 degrees higherthan the first mentioned temperature) and 44 F. of the dry bulb (or 6 degrees higher than the first mentioned temperature), the quantity ofwater vapor pres ent is also very nearly 2.4 grains to the cubic foot.Accordingly, if two thermometers whose stems are in juxtaposition be soconstructed that the divisions indicating a degree of difference oftemperature on the wet bulb thermometer stem are uniform and just doublethe size of the divisions indicating a degree of difference oftemperature on the uniformly divided stem of the dry bulb, it follows ofcourse that if the stems (placed vertically) are so put together thatthe 44 F. division on the dry bulb is horizontally opposite the 40 F.division on the wet bulb, then 54 F. on the dry bulb will be opposite 45F. on the wet bulb. It will also follow (as may be verified by referenceto any hygrometrical tables) that in each case, between the limits ofabout 35 F. and 56 F., when the column of liquid in the dry bulbthermometer is at the same, horizontal level as that in the wet bulbthermometer, no matter what the actual temperature indicated by therespective thermometers may be, the water vapor present in the air willbe very nearly 2.4 grains to the cubic inch. Whence then, if thehorizontal level of the liquid in the stem of the wet bulb thermometeris below the horizontal level of the liquid in the stem of the dry bulbthermometer, it is a sign that there is less water vapor in the air than2.4 grains to the cubic foot, and a frost will probably ensue. Simpleinspection will tell this at a glance, and it is not necessary visiblyto mark. the graduations on the two stems if only they are in realityduly constructed, and duly put into proper juxtaposition as abovedescribed. Of course in practice it is not essential that thethermometer stems should be placed vertically for use; they may be 'putin any position but the levels or surfaces of the tops or free ends ofthe columns of liquid must of course be observed perpendicularly to thelength of {"7 scribed and shown in the drawings.

the stems.

As above described, the invention is used with thermometers made of aliquid inclosed in glass tubes but it is obvious that thermometers madewith expansible solids may also be used provided that the co-etficientof expansion in each thermometer is tolerably uniform at differenttemperatures. An instrument on this plan is hereinafterI det is alsoevident that the use of the invention is not confined to frostprediction. In a manner precisely similar to that above described indetail and with the aid of the usual *hygrometrical tables, aninstrument can be i when a given ratio of dryness or humidity of theatmosphere has been reached, the instrument being suitable forindicating when a frost may be expected. Fig. 2 is a similar view toFig. 1 showing a modified arrangement.

In Fig. 1, a is a thermometer made of a glass stem and bulb charged witha liquid and having a dry bulb a and 7) is a second thermometer alsomade of a glass stem and bulb charged with a liquid having a wet bulb bments are so graduated that each division or portion of the tubecorresponding to'1'.

F. on the dry bulb stem at is half the length of a division or tubeportion corresponding to 1 F. on the wet bulb stem 7). The two"thermometers are put in juxtaposition on a board or carrier 6 so thatthe mark indicating 40 F. on the wet bulb stem b is put opposite themark indicating 44 F. on the dry bulb stem a. If then within the rangeof about 35 F. to 56 F. of the dry bulb reading, the column of fluid inthe wet bulb stem 1) sinks below the horizontal level, not the higher orlower reading in thermometric degrees than the other. The only point toobserve is whether the top of the liquid in the wet bulb instrument ishorizontally below the top of the liquid in the dry bulb in strument.Sometimes to suit the climatic characteristics of different countriesthe two tubes may be so calibrated or graduated thatthe relative lengthsof the divisions may be varied a little from that above mentioned so asto make 1 F. on the dry bulb a correspond say to 11-20ths of a degree onthe wet bulb stem 5. In either case the indication is sufficientlyapproximate to be practically useful. The invention is however notlimited to any exact ratio. Again, it may be desired to make aninstrument to show when the air of a room contains more than a givenpercentage of moisture, say 78% of saturation. To do this, dry and wetbulb thermometers are used as described, so cali brated that thirtythree Fahrenheit degree divisions on the dry bulb thermometer stemcorrespond to thirty two. Fahrenheit degree divisions on the wet bulbthermometer stem, and the two thermometer stems placed in juxtapositionso that the mark or division corresponding to 67 F. on the dry bulb stemstands opposite the mark or division corresponding to 63 F. on the wetbulb stem. Then, whenever the fluid in the wet bulb stemrisesthermometrically' above that in the dry bulb stem thiswill indicate thatthe limit of 78% of moisturewill (approximately) have been exceeded.These posi-' tions are of course only approximate, but they aresufiiciently true for practical and commercial purposes 1 and anyinstrument In this example, the two instrumay easily be made on thisplan by the use of hygrometrical tables such as the wellknown tables ofGlaisher, or again by the use of the well-known hygrometrical formulae.

It is obvious that the method of indicating the humidity of theatmosphere described is equally applicable to the expansion of solidsand to thermometers constructed on the principle of expansion of solids.Fig. 2 shows an instrument of this kind. In this example, twothermometers f and g are used each composed of two or more strips ofcompounded metals, in the manner usually employed for thermometers ofthis type, having different co-eflicients of expansion and provided witha pointer or index f or 9 The two thermometers are each fixed at one endto a base or support it and the thermometer g is provided with acovering 9 of absorbent material such as textile fabric that is keptcontinuously moistened with water like the wet bulb b of the instrumentshown in Fig. 1. The two thermometers f and g are made of such relativelength that in the case of an instrument designed to indicate when frostmay be expected, the index f of the thermometer f will move throughabout half the distance for each degree Fahrenheit that the index g ofthermometer 9 will move, as in the instrument shown in Fig. 1, so thatwhen the two indices f 9 come into line, as indicated in dotted lines, afrost may be expected. When this takes place, the indices, which may bemade of spring metal, can be caused to complete an electric circuit andcause an indication or signal to be given, for example, to set anelectric bell z' in action.

What I claim is 1. A hygroseope adapted to indicate by simpleinspection, the presence of a specified degree of moisture in the air,COIHPIIS- ing a dry thermometer adapted to indicate the temperature ofthe air and a wet thermometer adapted to indicate the temperature ofevaporating liquid in the air, the movable element of the wetthermometer having a movement bearing a substantially fixed ratio,different from unity, to the movement of the movable element of the drythermometer for each degree of variation of temperature, the movableelements of the two thermometers being arranged adjacent to each otherand so that the free end of the movable element of the wet thermometer,corresponding to some specified degree of temperature, will coincide inposition with that of the movable element of the dry thermometer whenthe specified degree of moisture in the air obtains, substantially asdescribed for the purpose specified.

2. A hygroscope adapted for frost indication, comprising dry and wetbulb thermometers of which the liquid column of the wet bulb thermometerhas a movement equal substantially to twice that of the dry bulbthermometer for each degree of variation of temperature, the stems ofthe two thermometers being arranged adjacent to each other and so thatthe level of the liquid column of the wet bulb thermometer correspondingto 40 F. will coincide with that of the liquid in the dry bulbthermometer corresponding to 44 F., substantially as described for thepurpose set forth.

Signed at London, England, this sixteenth day of January 1911.

HENRY HARDINGE SAMUEL CUNYNGHAME. Witnesses:

RIPLEY WILSON, C. P. LIDDON.

Gopies of this patent may be obtained for five cents each, by addressingthe "Commissioner of Patents,

Washington, D. O.

